1. Field of the Invention
This invention relates to a tray conveying method and apparatus in which for automatically attaching pull tabs to slide fastener sliders, a large number of trays each accommodating one of the pull tabs in row are previously stocked in stack, the loaded trays are supplied to a working station one at a time from the lowermost one of the stack, and the empty trays are collected.
2. Description of the Related Art
In conventional automatic assembling machines, it has been a common practice to use a bowl hopper feeder as a means for supplying pull tabs for slide fastener sliders. With this conventional feeder, the shape of the pull tabs which can be supplied from a row is limited to a plate-like shape having differences between upper and lower portions but identical between front and rear sides. If the form or design of the pull tabs is different between front and rear sides in view of fashionability or if the pull tabs have a unique form equipped with rubber, they cannot be supplied by the feeder. In the case where such unique pull tabs are to be supplied, it has been proposed to pre- place the pull tabs in a row on a tray and to convey the tray.
In a generally known tray conveying method, however, the lowermost loaded tray is separated from the waiting station where a large number of loaded trays are placed in a stack and is then supplied to the working station where parts are supplied to the automatic assembling machine by a robot or other means, and when the tray is emptied, the empty tray is discharged to the collecting station, opposite to the waiting station. This known method is exemplified by Japanese Patent Laid-Open Publication No. SHO 63-247221.
According to the conventional conveying method, the waiting, working and collecting stations are arranged basically in a row, and the row requires at least such a length that the trays to be conveyed can be placed in the individual stations. Assuming that this method is carried out by, for example, a rotary-table automatic assembling machine, various kinds of units are situated about a rotary table, each unit being located tangentially with respect to the rotary table to avoid any interference with adjacent units. This makes the distance between the working station and the placing station of the rotary table larger; as a result, when the parts are placed by a robot or other means, the extent to which the robot's arm is to be angularly moved will be greater so that it will take more time to supply the parts for assembling. Thus since such placing operation of the parts to the rotary table would take more time than placing operation of other parts, it is necessary to reduce the rate of rotation of the rotary table.